This invention relates generally to electrical property and burn-in tests for electronic parts, such as integrated circuits, and more particularly to a socket for providing an electrical connection between each terminal of an electronic part and an external device for removably loading the electronic part in the socket so that the leads of the socket are electrically connected to the respective terminals of the electronic part.
Generally, electronic parts such as IC packages, in which IC chips have been sealed with plastic, are subjected to a reliability test called an electric property test or a burn-in test prior to their shipment in order to distinguish between acceptable and unacceptable products.
In electric property tests, input and output characteristics of the IC chips, pulse properties, noise leeway, and the like are tested. In burn-in tests, on the other hand, IC packages that have passed the electric property test are arranged in an oven and are made to function at an elevated temperature, 125xc2x0 centigrade, for instance, and under a source voltage which is approximately 20% higher than the rated value. Those IC packages which fail in the burn-in test are removed as being unacceptable and only those others which continue functioning properly are shipped out as acceptable products.
In recent years, BGA (Ball Grid Array) packages having terminals made of solder balls positioned on the lower side of the package in a selected matrix, e.g., a zigzag fashion, have become popular as a desirable surface-loading type IC package. A BGA package provides advantages including features in which the terminals can be widely set while maintaining small outer dimensions and that the terminals are sturdy and resistant to deformation when they are brought into contact with other parts.
FIGS. 6(a) and 6(b) show a conventional socket for loading a BGA package for a burn-in test. Socket 101 has a square-shaped base 102 and a slider 103 for loading BGA package 100 is arranged for movement in a horizontal direction on the base. A cover 104, having an opening 104a therein, is received at the top of base 102. Cover 104 is vertically movable relative to base 102 by means of compression coil springs 105. A through hole is formed in slider 103 and base 102 corresponding to each solder ball 100a of the BGA package. A respective contact 106 for electrical connection with each solder ball 100a of the BGA package is arranged to extend through the through holes of base 102 and slider 103. Each contact 106 is made of an elongated metallic member with a pair of arms 106a and 106b facing upward. A protuberant part, not shown in the drawing, is provided on one arm of arms 106a and 106b (e.g., arm 106a) and, as this protuberant part engages the partition wall of slider 103, arms 106a and 106b are adapted to open and close upon sliding motion of the slider. A sliding mechanism for moving slider 103 in a direction which is in parallel with the bottom wall of base 102 is provided on opposite sides of the slider. The sliding mechanism includes a generally L-shaped lever member 108 rotatably mounted on each end of a shaft 107 provided at one side of base 102 (the right side in the drawings) and the short arm 108a of lever member 108 is rotatably linked to shaft 109 disposed in a vertically extending slot in slider 103 and which extends in parallel relation with shaft 107. A lever member 111 is rotatably mounted on each end of shaft 110 provided at the opposite side of base 102 and the tip of lever member 108 is slidingly attached by a pin 112 in a slot formed in each respective lever member 111 intermediate to its opposite ends. When cover 104 is not pressed, tip 111a of each lever member 111 is adapted to touch the protuberant part 104b of cover 104. Compression coil springs 113 are located in the vicinity of shaft 110 for biasing the slider toward the right as seen in the drawings.
In a socket made as described above, when cover 104 is pressed down from the state shown in FIG. 6(a) to the state shown in FIG. 6(b), lever members 108 and 111 rotate toward base 102 and shaft 109 transfers motion to slider 103 in conformity with the movement of lever member 108, thereby causing the slider to shift in the X-direction. As a result, arm 106a of the arms of each contact 106 starts opening due to engagement with the partition wall of slider 103. If, in this state, BGA package 100 is inserted through the central opening 104a of cover 104, BGA package 100 is positioned by guide 103c so that each solder ball 100a enters between arms 106a and 106b of a respective contact 106.
When the downward force on cover 104 is removed, lever members 108 and 111 rise and slider 103 is returned in the X+ direction by the force of coil springs 113 and the stored force of the contact arms, with a result that arms 106a and 106b of each contact 106 are closed and each solder ball 100a of BGA package 100 is held by arms 106a and 106b of a respective contact 106. Thus, each solder ball 100a of BGA package 100 is electrically connected to a respective contact 106.
With respect to a conventional socket 101 as described above, the linkage mechanism comprising the lever members 108 and 111, pin 112 and shafts 107, 109 and 110 is used to move slider 103. However, the number of parts involved is considerable and the construction becomes complicated, thereby requiring a number of assembly steps with concomitant assembly time before completion. Further, the use of the linkage mechanism adds to the size and weight of socket 101 making it larger and heavier than desired.
In copending applications, U.S. Ser. Nos. 09/694,636 and 09/850,622 filed respectively on Oct. 23, 2000 and May 7, 2001, and assigned to the assignee of the present invention, prior art linkage mechanisms of the type described are obviated by directly pressing the slider of the main socket body by means of a force applying member provided on a jig for loading the electronic part to be tested. The force applying member has a surface inclined at a selected angle and the force applying member of the jig is moved vertically toward and away from the socket, thereby making it possible for the slider of the main socket body to move in a direction normal to the movement of the force applying member, i.e., horizontal versus vertical directions.
In view of the fact that the amount of movement of the slider is therefore dependent upon the inclined angle of the force applying member of the jig that employs such a mechanism, there is a problem in that the degree of opening of the arms of the contact varies from one jig to another. Much of this depends on the precision with which the parts of the jig are made, with a result that the amount of opening of the contact arms cannot be controlled by the structure of the socket body alone.
An object of the present invention is to provide an apparatus which overcomes the above noted limitations of the prior art. Another object of the invention is the provision of a socket in which the amount of opening of the arm-like contact part of the contact member can be predetermined at a certain value by means of the socket itself without depending upon the accuracy of the various parts of the jig.
A socket made in accordance with the invention comprises a main socket body for removably receiving an electronic part in which the terminals of the electronic part are arranged according to a selected pattern. A plurality of contact members are arranged in the main socket body in conformity with the terminal pattern of the electronic part. Each contact member has a pair of contact arms, capable of elastically opening and closing to effect compressive electrical engagement with a respective connective terminal of the electronic part. A contact opening and closing member has an engagement part adapted for engagement with the contact members to move the contact arms in the opening and closing direction by receiving an external force that is approximately in parallel with the opening and closing direction of the contact arms applied at a cam follower portion of the contact opening and closing member. A force transfer cam member, provided at a selected location on the edge portion of the main socket body, has a cam surface that engages the cam follower portion of the contact opening and closing member at a selected angle and which is movable in a direction which crosses, at approximately a right angle, the moving direction of the contact opening and closing member so as to cam the cam follower portion, while sliding there against. According to a feature of the invention, the cam member is mounted on the main socket body, with the contact arms of each contact member being opened by the action of the cam member. This arrangement provides the ability to control the accuracy of the cam follower portion of the contact opening and closing member and the position of the cam member within the socket without depending upon the accuracy of the parts of the separately provided jig so that the amount of the opening of the contact arms of each contact member can be determined more consistently. According to another feature of the invention, the cam member is formed as a button type member having a head of a size suitable to enable one to press the cam member with a finger, for example, so that one can press down the cam member with one hand in connection with unloading the electronic part from the socket. Thus, the operability of a manual unloading operation can be improved by locating the cam member on the edge portion of the main socket body so that the seating area for the electronic part can be more fully exposed to further improve the operability of the unloading operation. According to yet another feature of the invention, the main socket body can be formed in a rectangular configuration, such as in the shape of a square, with the contact opening and closing member being arranged so that the engagement of the contact opening and closing member moves the arms of the contact members in a direction which is in parallel with the imaginary diagonal line of the main socket body. The contact opening and closing member itself can be guided in the diagonal direction and in the preferred embodiment, the cam member is arranged at one corner on the diagonal line of the main socket body.
Accordingly, a single cam member is sufficient to move the contact opening and closing member. As a consequence of this, the number of parts whose accuracy has to be controlled is reduced, thereby making it possible to better control the amount of opening of the contact arms of each contact member.
According to a feature of the invention, a plurality of depressions or longitudinal grooves of a selected size can be formed in the cam surface of the cam member to reduce the surface area of the cam member which engages the cam follower portion of the contact opening and closing member. Accordingly, it becomes possible to reduce the frictional resistance when the cam member slides over the cam follower portion of the contact opening and closing member.
According to another feature, an electronic part holding mechanism is provided which is movable while maintaining a state facing the main socket body of the socket in order to load an electronic part. The holding mechanism is part of a contact opening and closing jig that has a force applying part that is engageable with the cam member of the socket. Thus, it is only necessary to provide one force applying location on the contact opening and closing jig for effecting movement of the contact opening and closing member by means of the cam member. Accordingly, it becomes possible to reduce the size of the contact opening and closing jig itself and the number of parts of the contact opening and closing jig.